The invention relates to a storage apparatus and a data writing method, for example, suitable for use in a storage system having a feature of dynamically allocating a storage area in a volume for storing data.
A storage system having a feature of dynamically allocating a storage area in a volume for storing data has conventionally been known, and various techniques relating to that feature have also been proposed.
For example, in JP2003-015915 A, the full capacity of physical volume to be provided to a host computer is not initially prepared, but a required physical disk is added if the disk usage approaches the upper limit of the capacity, thus dynamically varying the storage capacity provided to the host computer.
In the above mentioned storage system, that technique does not create, from a pool area, a logical volume of a fixed capacity, but firstly provides a virtual logical volume to the host computer. After that, in response to I/O (input/output) from the host computer, a storage area is dynamically allocated in predetermined units from a pool area, which is a physical source, to the virtual logical volume, thus dynamically expanding the capacity.
Meanwhile, a storage system having a virtualization feature where a higher-level storage apparatus is connected to an external storage apparatus to use the external storage apparatus as an internal storage device by mapping the external storage apparatus has also been known, and various techniques relating to that technique have been proposed too.
For example, in JP2007-102439 A, a storage area provided by the higher storage apparatus itself and a storage area provided by the external storage apparatus connected to the higher-level storage apparatus and used as an internal storage device are collectively managed by the higher-level storage apparatus, and data is read/written by having the higher-level storage apparatus sort data I/O requests from the host computer and sending them to a relevant external storage apparatus.
However, even if the external storage apparatus has the storage area dynamic allocation feature, the higher-level storage apparatus writes data to the internal storage devices, not taking into consideration the storage area dynamic allocation feature the external storage apparatus has.
Therefore, a storage area of too large a size with respect to the data to be written may be allocated to the internal storage device, and as a result, a wasteful area is generated in the storage area allocated to the internal storage device, so the storage area allocation is inefficient.